The language addon is now updated. There is still untranslated "all day" text in the day and week views so if you have a good translation for it (note that there is a very limited space available) I can add it to the addon as well.

Month view: = Mese:
Week view: = Settimana:
Day view: = Giorno:
Translate: = Traduci:
All day = The best translation is "Tutto il giorno" (This translation is also adopted by Google Calendar) but I think there is enough space. Therefore, if it is not enough space, I'll try something else to propose